Increase the removal rate of Cu at CMP
System Description: Cu CMP Process
During copper CMP, the wafer is held face-down by the carrier head and pressed against a rotating polishing pad. Slurry is continuously supplied to the contact area between the wafer and the pad. The slurry contains water, chemical additives, abrasive particles, and H₂O₂, which oxidizes the copper surface.
The oxidized copper layer is mechanically removed by the polishing pad and abrasive particles, while the slurry carries away the reaction products and removed material. The pad grooves distribute fresh slurry across the polishing area and help remove spent slurry. A diamond conditioning disk restores the pad surface and maintains its polishing capability. Sensors and the tool controller monitor the process and determine when the required amount of copper has been removed.
Product
- Cu overburden
Polishing mechanism
- Polishing pad
- Pad asperities
- Pad grooves
- Platen
- Carrier head
- Carrier membrane
- Retaining ring
Chemistry
- H₂O₂
- Abrasive particles
- Complexing agent
- Corrosion inhibitor
- Water/slurry medium
Supporting components
- Diamond conditioning disk
- Endpoint detection system
Essential functions for the model
Use active verbs rather than general connections:
- Carrier head presses wafer
- Carrier membrane distributes pressure across wafer
- Retaining ring retains wafer
- Platen moves polishing pad
- Polishing pad applies friction to oxide layer
- Pad asperities shear oxide layer
- Pad grooves distribute slurry
- Pad grooves evacuate spent slurry
- H₂O₂ oxidizes Cu
- H₂O₂ forms/passivates Cu surface
- Complexing agent complexes Cu ions
- Abrasive particles disrupt oxide layer
- Slurry transports removed material
- Conditioning disk restores pad microtexture
- Conditioning disk wears polishing pad
- Endpoint sensor measures remaining Cu
- Controller terminates polishing
H₂O₂ forms Cu oxide → oxide expands and passivates Cu → pad asperities and abrasives remove oxide → complexing agent stabilizes dissolved Cu → slurry carries reaction products away.
Operational Effectiveness – OE
Effective
Ineffective
OE 2.12
Operational Perfectness - OP
Basic functions
Components
Supersystems
OP 0.27
Carrier head | 21 |
Slurry | 8 |
Cu Overburden | 7 |
Retaining ring | 5 |
Abrasive particles | 5 |
Carrier membrane | 5 |
H2O2 solution | 5 24 |
CuO layer | 3 3 |
Polishing pad | 3 |
Pad grooves | 2 |
What we learned is:
More H₂O₂ does not necessarily mean faster Cu removal. Excess peroxide rapidly converts the Cu surface into a thick, continuous oxide layer. Because Cu₂O and CuO occupy about 1.7–1.8 times the volume of the consumed copper, the protective layer grows quickly, passivates the surface, and must be mechanically stripped before polishing can continue.
When the oxidation rate increases, we need to increase the mechanical removal rate: increase the pad rotation, increase the concentration of the abrasive particles in the slurry. It is not make any sense to increase the concentration of one component, such as H2O2, and expect for the overall increase in the removal rate. Some other parameter should be changed to adjust the mechanical part of the process.
If | We increase the concentration of H2O2 in the slurry |
|---|---|
Then | The oxidation process will be faster - H2O2 solution interacts with the Cu Overburden to stimulate the easy removal of Cu and CuO |
But | A thick layer of CuO will request more time to polish - A thick layer of CuO2 is formed, which causes the system to remove 2-times more material because CuO is about 2 times low in density compared to Cu. |
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